1. Field of the Invention
This invention relates to improvements in rock-breaking apparatus of the general type described in Australian patent specification no. AU-B-27994/77 (522890).
2. Description of the Prior Art
Rock breaking apparatus of the type described in AU-B-27994/77 includes a rock-breaking tool, a tool housing having a bore therethrough, in which the tool body is mounted for limited movement axial to the bore, a weight designed to fall under the influence of gravity to impart an impulse to said tool, and means to raise the weight.
Very large forces are generated in the use of said apparatus. They are often sufficient to destroy the upper collar on the tool body as it is driven against the upper edge of the bore, which collar serves to limit downward movement of the tool. This means that the tool must be replaced, which is an expensive and time-consuming operation. In the specification of Australian patent specification no. AU-B-90861/82 (536689), corresponding to U.S. Pat. No. 4,562,974 there is suggested a complex arrangement for cushioning the effect on the apparatus as a whole of the force applied to the tool, by providing a resiliently-mounted telescopic member at the lower end of a guide column, through which the weight falls. However, the specification does not address the problem of the effect of the force on the tool per se.